1. Field of the Invention
The present invention is generally concerned with torsional damper devices comprising at least two coaxial parts disposed to rotate relative to one another within defined limits of relative angular displacement against elastic means, commonly called circumferentially acting elastic means, adapted to be operative circumferentially between them for part at least of such relative angular displacement.
2. Description of the Prior Art
As is known, this type torsional damper device is normally incorporated in the design of a clutch disk, particularly for automobile vehicles, in which case one of its rotary parts carries a friction disk designed to be constrained to rotate with a first shaft, in practice a driving shaft and the motor output shaft in the case of an automobile vehicle, whereas another comprises a hub through which it is adapted to be constrained to rotate with a second shaft, in practice a driven shaft and the gearbox input shaft in the case of an automobile vehicle.
A device of this kind is used to permit regulated transmission of rotational torque applied to one of its rotary parts where the other is itself subject to a rotational torque, that is to say, to filter vibrations which may arise at any point in the kinematic system in which it is incorporated, extending from the motor to the driven road wheels in the case of an automobile vehicle.
The present invention is more particularly directed to the case where at least three coaxial parts are employed in the construction of a torsional damper device of this kind, namely, in the direction from the axis of the device to its periphery, a first part comprising a hub, being the part designed to be constrained to rotate with the gearbox input shaft in the case of an automobile vehicle, a second part comprising at least one flange, commonly called the hub flange, forming a transverse annular part around said hub with, between it and the hub, meshing means implemented with clearance, and a third part also comprising at least one flange which, like the hub flange, to which it is parallel, forms a transverse annular part around the hub, but without any direct relationship therewith, this third part being that carrying the friction disk in the case of an automobile vehicle.
In practice this third part comprises two flanges parallel to and axially spaced from one another, one on each side of the hub flange, coupled together by axial spacers passing through openings formed in the hub flange for this purpose.
These flanges, which are the outermost flanges in the axial sense in the resulting torsional damper device, are commonly called "guide rings" since the circumferentially acting elastic means disposed between the third coaxial part of which they form part and the second coaxial part, in this instance the hub flange, intermediate the third coaxial part and the first coaxial part, comprise circumferentially distributed elastic members which they retain or, in other words guide, featuring openings in which the elastic members are individually and at least partially accommodated.
One problem to be solved in producing three-part torsional damper devices of this kind results from the necessity to reconcile two apparently contradicatory requirements.
The first of these requirements relates to the fact that to minimize or even reduce certain sources of noise, more precisely the noise commonly called "trash" noise arising, for example, when the driver of the vehicle concerned depresses or releases the accelerator pedal and resulting from gears in the gearbox of the vehicle impacting on one another under load, it appears desirable, as is confirmed by experience, that the circumferentially acting elastic means disposed between the second and third coaxial parts of a torsional damper device of this kind feature a relatively low stiffness, in practice of not more than 1 m.daN per degree.
As a corollary to this, a second requirement which normally has to be met, and which is in this instance imperative, that at the end of angular displacement between said second and third parts, and thus, taking an overall view, between the first and the third parts, the maximum permissible torque is greater than the most usual maximum motor torque values.
These are frequently of the order of 15 to 17 m.daN.
For safety reasons, it is therefore desirable that the maximum torque that can be transmitted between the first and third coaxial parts of a torsional damper device of the kind in question should be of the order of 20 m.daN, for example.
In torsional damper devices of the kind in question known at present, the maximum angular displacement possible between the second and third coaxial parts is limited.
The limitation as to this angular displacement is embodied in the circumferential extent that can be given to the openings formed in the hub flange constituting the second part for the axial spacers coupling together the two flanges or guide rings constituting the first part to pass through.
Beyond a certain circumferential dimensions, these openings inevitably reduce to an unacceptable degree the mechanical strength of the hub flange, compromising the service life of the device.
In practice, in torsional damper devices of the kind in question known at present, the angular displacement between the second and third coaxial parts is more often than not 10 degrees of less.
Thus if, in order to minimize "trash" noise, there are employed between these second and third parts circumferentially acting elastic means having only moderate stiffness, of the order of 1 m.daN per degree, for example, as indicated above, the maximum permissible torque at the end of angular displacement of the device, ignoring that due to the circumferentially acting elastic means disposed between the first and second parts (which is very small, these circumferentially acting elastic means themselves having only a relatively low stiffness for other reasons, specifically to filter so-called neutral or idling noise), is at most of the order of 10 m.daN, which is insufficient.
A general object of the present invention is an arrangement whereby this difficulty may be overcome and hence the contradictory requirements reconciled.